Timber itself is becoming rarer and rarer and types of timber having the same properties are becoming even more rare. On the other hand, petroleum appears to be far more available than was hitherto assumed. Recent finds in Saudi Arabia make it appear that petroleum production is assured at least until the century after next. This means that plastic is available. The problems of what is to happen with used plastic are very pressing even now. So-called recycling presents great problems, since nobody can think of a satisfactory way of putting large quantities of plastic to renewed use.